Percentage Value Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching percentage value, ported and verified for JavaScript. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Percentage Value
// ReDoS-safe | RegexVault — Finance > Currency & Money

const percentageValueRegex = /^-?(?:100(?:\.0{1,4})?|(?:[0-9]{1,2}(?:\.[0-9]{1,4})?))%?$/;

function validatePercentageValue(input: string): boolean {
  return percentageValueRegex.test(input);
}

// Example
console.log(validatePercentageValue("0")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Currency & Money category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Constrained to -100 to 100. For percentages that can exceed 100% (e.g., year-over-year growth), remove the upper bound: ^-?[0-9]+(?:\.[0-9]{1,4})?%?$ . The percent sign is optional for API input.